Since the investigation of the first known outbreak of Ebola hemorrhagic fever in 1976 in Yambuku area, Zaire (now Democratic Republic of Congo), which was largely due to unsafe medical injections, I have been fascinated by the sometimes devastating consequences of medical injections. Add to this the finding that between 1976 and 1986 HIV prevalence remained unchanged at 0.8% in the same region (1), and I read Jacques Pepin's The Origins of AIDS in one go.
Pepin, an infectious disease specialist at the Université de Sherbrooke, Quebec, has vast experience as a clinician and epidemiologist in Africa. In this concise book, he draws on three decades of scientific and historical research to comprehensively address one of the big enigmas of medical history: the origin of AIDS—a disease first reported only as recently as 1981. Thanks to extraordinarily meticulous virological, genetic, and ecological studies, we have very strong evidence that HIV-1 stems from the genetically very close strains of simian immunodeficiency virus (SIVcpz) of the chimpanzee Pan troglodytes troglodytes from central Africa. However, the course and causes of the initial spread of HIV-1 in humans after the virus crossed host species remain unclear, with very few of the details firmly established.
Pepin confronts us in great detail with some puzzling facts that suggest the epidemic that to date has infected over 60 million people originated with fewer than ten people scattered over central Africa. During the first decades of the 20th century, each of these ten became infected with one of four genetic groups of HIV-1 (M, N, O, and P) from chimpanzees. Pepin's central thesis is that medical injections and procedures jump-started the HIV epidemic in Africa, building up a critical mass of HIV-infected individuals. This mass then ultimately gave rise to a predominantly sexually transmitted epidemic. He agrees with most other experts in the field that today medical injections play only a minor role in the global spread of HIV. And he summarizes the overwhelming evidence against Edward Hooper's hypothesis (2) that the emergence of the disease “was triggered by the contamination of an oral polio vaccine with a simian immunodeficiency virus through the use of chimpanzee cells during vaccine production.”
The author makes some brave assumptions and extrapolations from mostly isolated facts—just as paleontologists have no choice but to draw a complete skeleton on the basis of a few pieces of bones, date it, and estimate the place of the new individual in human evolution. Tapping the archives and medical literature of the colonial powers in West and Central Africa, he presents a plethora of details going back to as far as the beginning of the 20th century. They reveal little-known and sometimes shocking elements of not-so-distant medical history, such as a French colonial surgeon implanting chimpanzee testicles in men seeking eternal youth and experimental injections of chimpanzee blood in patients with syphilis in Belgium.
On the basis of both contemporary concepts of transmissibility and historic demographic and behavioral data, Pepin suggests that the efficiency of sexual transmission of HIV-1 was too low to enable the virus to spread beyond a few individuals. He then shows how mass campaigns organized by French and Belgian colonial administrations to treat tropical diseases such as yaws, sleeping sickness, leprosy, syphilis, and malaria exposed hundreds of thousands of people to intravenous or intramuscular injections with potentially contaminated needles and glass syringes. These campaigns affected both rural and urban populations, and in areas of habitat of P. troglodytes troglodytes north of the Congo River they may have been the defining factor in slowly building up enough infected individuals to sustain human HIV-1 infection. For decades the reproductive rate Ro of HIV-1 in Africa was clearly around 1, and AIDS remained at very low prevalence levels. But eventually a fatal combination of urbanization, prostitution, and mass treatment of sexually transmitted infections generated a perfect storm in Léopoldville (now Kinshasa), the capital of Belgian Congo, for amplifying the spread of the disease. The presence of over 4000 Haitian United Nations employees during the turbulent years after the independence of Congo in 1960 probably led to the introduction of HIV-1 in Haiti. The rest of the story is well documented.
The Origins of AIDS presents the defining pandemic of our modern times as a tragedy embedded in colonization, urbanization, and public health campaigns. It reminds us that well-intentioned human interventions can have unpredictable and disastrous microbiologic consequences. Extensively referenced, the well-written book reads like a detective story, while at the same time providing a didactic introduction to epidemiology and evolutionary genetics. As far as the origins of AIDS are concerned, unless some completely new evidence emerges, it will be difficult to come up with a better explanation than Pepin's. The role of medical injections in the initial spread of HIV in Africa is quite plausible. It is certainly consistent with more recent outbreaks of HIV among injecting drug users seen in various countries and with the massive iatrogenic epidemic of hepatitis C virus infection in Egypt as a result of mass treatment of schistosomiasis. Nonetheless, the actual key events in the spread of HIV-1 may not be covered by a rational model of average probabilities of transmission and behaviors As Pepin himself comments, we may never know whether “the pandemic was in essence caused by an unpredictable factor: bad luck.”
References and Notes
2. E. Hooper, The River: A Journey to the Source of HIV and AIDS (Penguin, London, 1999); reviewed in R. A. Weiss, Science 286, 1305 (1999). FREE Full Text